This invention relates to a method and an apparatus for the three-dimensional digitization of objects, wherein a pattern is projected onto the object by means of a projector, and the pattern is detected with one or more cameras. Projector and cameras usually are constructionally integrated in a so-called 3D sensor. In particular the digitization by means of white-light strip projection is already known. In this method, the projector projects a strip image onto the object to be digitized. The strip image then is detected by the one or more cameras. The local object data, i.e. the three-dimensional object geometry in the local coordinate system of the 3D sensor, can be determined therefrom. For a complete or large-surface digitization of an object, the 3D sensor regularly must be moved into different recording positions, and the local object data at the individual recording positions must be combined in a global coordinate system, so as to be able in particular to combine the measurement results at the individual recording positions to a total measurement result for the entire surface measured. This requires a precise detection of the individual recording positions in a global coordinate system.
In the white-light strip projection, the global detection of the individual recording positions usually is effected by photogrammetric measurement of reference marks, which are attached or adhered to the object to be digitized and are separately measured with a photogrammetry system. The photogrammetric measurement of the reference marks performed before measurement with the 3D sensor provides a set of reference points, by means of which the local measurements of the 3D sensor at the individual recording positions can be transformed into a uniform, global coordinate system.
Although the photogrammetric measurement of the reference marks provides a high accuracy, it is disadvantageous because of the effort involved in preparing the object with the marks and because of the separate measurement operation. Alternatively, projected reference marks are used, which are projected onto the object to be digitized by means of an external separate projector. However, this involves the disadvantage of a reduced accuracy as compared to adhered marks, since the shape of the projected marks is influenced by the geometry of the object.